This invention relates to the art of temperature control and has particular relationship to set-back control of temperature sensing apparatus for a region to set-back the temperature in the region. In set-back control the temperature of a region under the control of a thermostat, typically of a room under the control of a room thermostat, is set-back during certain intervals by local heating of the air enveloping the thermostat. The thermostat responds to the increased temperature which it senses to set-back the temperature in the region. The purpose of such a set-back system is to effect a saving in fuel without having to modify the electrical wiring of the existing house temperature control apparatus.
The most up to date prior art on temperature set-back is typified by Buckwalter patent. Typical prior art apparatus such as Buckwalter's is complicated. For example, Buckwalter's control includes a bi-metal switch (40 FIG. 3) which turns the local heater (28) off and on during the set-back interval.
It is an object of this invention to overcome the disadvantages of the prior art and to provide a low-cost set-back control of uncomplicated structure, to be used in conjunction with an existing room thermostat and which shall effectuate the set-back control and shall not be susceptible to instability due to surrounding air currents.